britbulls

Hi I recently acquired a british bullldog. we also have another dog who is a crossbreed. Our crossbreed has issues with fleas and also reacts to most flea treatments. Our bulldog now has some fleas as well. I was told about a flea injection given annually, and this prevents fleas and heartworm. Can anyone advise me on this and letmeknow of their experience with it if they have used it?